Field of Invention
The present invention relates to a urea supply system for supplying urea water solution (hereinafter, referred to as “urea”) to a selective catalyst reduction (hereinafter, referred to as “SCR”) device for after-treatment of exhaust gas.
Description of Related Art
Recently, as problems regarding environmental pollution have become main issues, electric vehicles, hydrogen vehicles, solar vehicles, and hybrid vehicles, which are environmentally-friendly vehicles that do not use fossil fuel, have been actively developed and commercially available in the automotive industries as well.
However, despite the appearance of the environmentally-friendly vehicles, vehicles, which use gasoline or diesel as fuel, are still mainly used, and is also expected to keep their place even in the future.
In the case of the aforementioned vehicle having an internal combustion engine that uses fossil fuel such as gasoline or diesel, there is a problem in that environmental pollution caused by exhaust gas is severe.
In general, exhaust systems of diesel engines are provided with exhaust gas after-treatment devices such as a diesel oxidation catalyst (DOC), a diesel particulate matter filter (DPF), selective catalyst reduction (SCR), and a lean NOx trap (LNT) in order to reduce pollutants such as carbon monoxide, hydrocarbon, particulate matters, and nitrogen oxide that are included in exhaust gas.
Among the aforementioned exhaust gas after-treatment devices, an exhaust gas after-treatment device using the SCR (hereinafter, referred to as “SCR device”) serves to inject a reducing agent such as urea into an exhaust pipe, and reduce nitrogen oxide in the exhaust gas into nitrogen and oxygen.
That is, when the SCR device injects a reducing agent into the exhaust pipe, the reducing agent is converted into ammonia by heat of the exhaust gas, and nitrogen oxide may be reduced into nitrogen gas and water by a catalyst reaction between nitrogen oxide and ammonia in the exhaust gas which is caused by an SCR catalyst.
In order to inject the urea into the exhaust pipe, a urea supply system is required to supply the urea to the SCR device.
Meanwhile, a urea tank is provided with a urea injection device for injecting the urea into the tank, and the urea injection device is provided with a urea filler neck, and a leveling pipe that connects the urea tank and the urea filler neck.
In the urea injection device, when the urea is injected into the urea tank through the urea filler neck, ammonia gas in the urea tank may be discharged to an injection port of the urea filler neck through a leveling pipe.
The urea causes ammonia gas which is a toxic material that is harmful to the human body. Therefore, the ammonia gas, which is harmful to the human body, is excessively emitted to the injection port of the urea filler neck, and thus causing displeasure to a user, and damaging the user's health. Accordingly, ISO regulations (ISO22241-5) restrict emission concentration of ammonia gas at the urea injection port to 15 PPM or less.
Moreover, the ammonia gas in the urea tank is emitted through a ventilation valve, but the urea concentration of the urea solution deteriorates while the urea in the urea tank is exposed to the atmosphere, which may cause inferiority of the urea, which may cause the urea to be inferior and easily frozen in the winter.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.